Fluke i400s ac current clamp fluke fluke i400s the i400s is compatible with any instrument capable of ac millivolt measurements it can accept a standard bnc connector and has an input impedance of greater than or equal to 1 m omega in parallel with a maximum of 47pf the current clamp can also be used with digital multimeters using a bnc to banana jack adaptor fluke i400s ac current clamp 400a